.TH BUS_READ 3 BUS
.SH NAME
bus_read, bus_read_timed - Listen for new messages a bus
.SH SYNOPSIS
.LP
.nf
#include <bus.h>
.P
int bus_read(const bus_t *\fIbus\fP, int (*\fIcallback\fP)(const char *\fImessage\fP, void *\fIuser_data\fP),
void *\fIuser_data\fP);
int bus_read_timed(const bus_t *\fIbus\fP, int (*\fIcallback\fP)(const char *\fImessage\fP, void *\fIuser_data\fP),
void *\fIuser_data\fP, const struct timespec *\fItimeout\fP, clockid_t \fIclockid\fP);
.fi
.SH DESCRIPTION
The
.BR bus_read ()
function waits for new message to be sent on the bus specified in
\fIbus\fP, as provieded by a previous call to the
.BR bus_open ()
function. Once a message is received, the \fIcallback\fP function is
invoked. The \fImessage\fP argument to the callback is the received
message, and \fIuser_data\fP for \fIcallback\fP should be
\fIuser_data\fP from
.BR bus_read ().
However, once
.BR bus_read ()
has ensured that it will receive any message sent on the bus, it shall
invoke the \fIcallback\fP function with \fImessage\fP set to \fINULL\fP,
to notify the process that it can perform any action that requires that
it is listening on the bus.
.PP
After \fIcallback\fP returns, \fImessage\fP may be override. Therefore
\fIcallback\fP should copy \fImessage\fP and start a new thread that
uses the copy of \fImessage\fP. \fIcallback\fP shall return -1 on
failure, 0 if
.BR bus_read ()
should stop listening or 1 if
.BR bus_read ()
should continue listening.
.PP
The
.BR bus_read_timed ()
function behaves like
.BR bus_read (),
except it will automatically fail and set \fIerrno\fP to \fBEAGAIN\fP
when the specified time has passed. The time is specified as an
absolute time using the parameter \fItimeout\fP. The behaviour is
unspecified if \fItimeout\fP is \fINULL\fP. \fItimeout\fP is measured
with the clock whose ID is specified by the \fIclockid\fP parameter.
This clock must be a predicitable clock.
.SH RETURN VALUES
Upon successful completion, these functions returns 0. Otherwise the
function returns -1 and sets \fIerrno\fP to indicate the error.
.SH ERRORS
The
.BR bus_read (3)
function may fail and set \fIerrno\fP to any of the errors specified for
.BR semop (3).
The
.BR bus_read_timed (3)
function may also set \fIerrno\fP to any of the errors specified for
.BR clock_gettime (3).
.SH SEE ALSO
.BR bus-create (1),
.BR bus (5),
.BR libbus (7),
.BR bus_open (3),
.BR bus_write (3),
.BR bus_poll (3),
.BR semop (3),
.BR clock_gettime (3)
